1. Field of the Invention
The present invention relates to a disk recording medium such as optical disk and photomagnetic disk.
2. Description of the Related Art
As a disk recording medium which is used left unreceived in a cartridge, i.e., in a so-called single form there is known one comprising a printing surface provided on one side thereof and a recording surface provided on the other. A printing layer is formed by a printing ink on the printing surface. The printing surface displays the contents of data recorded in the disk recording medium. As such a disk recording medium there is known an optical disk such as musical CD and CD-R.
Such a disk recording medium is often received and stored in a plastic case when not in use. The plastic case also receives an index card (title card) indicating the contents of data recorded in the disk recording medium.
For example, when a disk recording medium is stored in a plastic case at a proper temperature and humidity for a long period of time, fungi can grow on the index card or disk recording medium (particularly on the printing surface) because the paper fiber constituting the index card or the printing layer in the disk recording medium contains nutrient. Further, when the user handles the index card, the disk recording medium and the plastic case, they are stained with dirt or oil of the user's hand that causes the proliferation of fungi.
In particular, since the paper fiber constituting the index card exerts a great moisture-retaining effect, fungi which has grown on the index card can easily move to the surroundings. When fungi which has grown on the index card moves to the plastic case or disk recording medium, fungi can acceleratedly grow on the plastic case or the printing surface of the disk recording medium.
The printing surface of the disk recording medium stained with fungi apparently has an outstanding dirt that lowers the credit thereof with the user and hence the commercial value. Further, when the recording surface of the disk recording medium is stained with fungi which has moved from the printing surface or the like, normal reading and writing of recorded data cannot be performed.
The recent high capacity optical disk (e.g., DVD) is required to use a recording light beam having a very small spot diameter in order to accomplish high density recording. To this end, a laser source having a short wavelength is used. Alternatively, the aperture of lens is raised. Such an optical disk tends to have a very small distance between the recording surface and the condenser. When the recording surface of the optical disk has fungi, the fungi can move to laser pick up lens or the interior of drive, making it unlikely that normal reading and writing of recorded data can he performed.